1. Technical Field
The present invention relates to a thin-film piezoelectric element including a thin-film piezoelectric material, a thin-film piezoelectric actuator and a thin-film piezoelectric sensor each including the thin-film piezoelectric element, and a hard disk drive and an ink jet printer apparatus each including the thin-film piezoelectric actuator.
2. Related Background Art
In recent years, there have been advances in practical use of thin-film piezoelectric elements including thin-film piezoelectric materials, instead of bulk piezoelectric materials. Examples thereof include gyroscope sensors, pressure sensors, pulse wave sensors, shock sensors, and microphones, which serve as piezoelectric sensors using a piezoelectric effect, in which a force applied to a piezoelectric thin film is converted into a voltage; head assemblies for hard disk drives and ink jet print heads, which serve as piezoelectric actuators using an inverse piezoelectric effect, in which a piezoelectric thin film is deformed by the application of a voltage to the piezoelectric thin film; and speakers, beepers, and resonators, which also use the inverse piezoelectric effect.
A reduction in the thickness of piezoelectric materials enables the miniaturization of elements and widens the field of application. Furthermore, many elements can be collectively produced on a substrate, thereby increasing the mass productivity. There are many advantages in performance, for example, improvement in sensitivity as a sensor.
In the case where a piezoelectric thin film included in a thin-film piezoelectric element has a predetermined crystal structure, satisfactory piezoelectric properties are provided. Further improvement in crystallinity enables a piezoelectric constant to be further improved. Examples of a method for improving the crystallinity include the optimization of deposition conditions of deposition apparatuses configured to form piezoelectric thin films by sputtering, CVD, and so forth; and a method in which an underlying surface where a piezoelectric thin film will be formed is subjected to treatment.
PTL 1 states that a reduction in the surface roughness of a surface of an electrode layer serving as a base layer of a piezoelectric thin film improves the crystal orientation of the piezoelectric thin film during growth to increase the piezoelectric properties.
PTL 2 states that a piezoelectric thin film having high crystallinity optimum for improving a piezoelectric constant is formed by optimizing the crystal grain size of the piezoelectric thin film and the roughness of the piezoelectric thin film itself.
PTL 3 states that a piezoelectric thin film having an improved piezoelectric constant and resistance to dielectric breakdown is formed by suppressing a P-V value, which is defined by a peak-to-valley difference on the entire surface of the piezoelectric thin film.
[PTL 1] Japanese Unexamined Patent Application Publication No. 2010-161330
[PTL 2] Japanese Unexamined Patent Application Publication No. 09-298324
[PTL 3] Japanese Unexamined Patent Application Publication No. 2010-219493